Ramsey Prize Talk: Searching for the Electric Dipole Moment of the Electron: Ramsey, ACME and the future

Norman Ramsey pioneered a dazzling array of techniques and ideas that continue to guide precision searches for physics beyond the standard model. Similarly, his manners and style set the tone for the field of AMO experiment, a research culture that I and thousands of researchers have benefited from and aim to continue. Just one contribution is that of searches for the electric dipole moments of the fundamental particles. First posed as a “what if?” question – is microscopic time reversal violation present in the universe – now EDM searches are powerful probes of CP-violating (CP-v) beyond the Standard Model physics at the 3-30 TeV level. New sources of CP-v with new particles can address three fundamental questions in physics: why isn't the Higgs mass much larger, what is dark matter, and why is there a matter-antimatter asymmetry of the universe? Ramsey not only launched the field of EDM searches but also developed a key tool, the separated oscillatory field (SOF) method, now so ingrained in the quantum science paradigm. The goal of these types of precision measurements is to measure quantum energy-level spacings as precisely as possible by use of coherent excitation. Thus, precision measurement is fundamentally limited by the coherence time. In the SOF method, this is the spin precession time between the excitation and readout regions. In modern AMO, there are two levels of technology for achieving long coherence times, molecular beams, also pioneered by Ramsey, and trapping.



I will give a brief description of ACME, which twice improved by x10 the limit on the electron EDM. Combining a (then) new type of radical molecule cold beam source with high precision laser quantum state preparation and readout of spin-precession, ACME brought together new methods and the molecular beam approach pioneered by Ramsey. Impacts of our EDM limits on the understanding of particle physics will be presented. I will give an overview of the directions the field of EDM searches is taking, including the laser cooling of molecules and use of new species to reach the PeV mass range for BSM particles with CP-v interactions. Finally, I will discuss polyatomic molecules, which have rich quantum state structures that are useful for precision measurement.